1. Field of the Invention
This invention relates to novel ionic phosphites and the use thereof as ligands in homogenous transition metal catalyzed processes, especially hydroformylation.
2. Background of the Invention
Use of organic solubilized transition metal ligand complex catalysts is well known in the art of olefin hydroformylation, hydrosilation, hydrogenation, and oligomerization. In particular, olefinic compounds are hydroformylated with carbon monoxide and hydrogen to produce aldehydes in the presence of organic solubilized transition metal-phosphorus ligand complex catalysts.
It is known that the particular phosphorus ligand employed in such catalyzed hydroformylation processes may have a direct effect on the success of any given process. Moreover, selection of a particular phosphorus ligand to be used in any such transition metal catalyzed hydroformylation process depends upon the result desired, since the best overall processing efficiency may require a compromise between numerous factors. For example, in hydroformylation, such factors as aldehyde product selectivity (i.e., normal to branched chain aldehyde product ratio), catalyst reactivity and stability, and ligand stability often are of major concern in the selection of the desired phosphorus ligand to be employed.
For instance, U.S. Pat. No. 3,527,809 teaches how alpha-olefins can be selectively hydroformylated with rhodium-triorganophosphine or triorganophosphite ligand complexes to produce oxygenated products rich in normal aldehydes, while U.S. Pat. Nos. 4,148,830 and 4,247,486 disclose both liquid and gas recycle operations directed to the same result using a rhodium triarylphosphine ligand complex catalyst. U.S. Pat. No. 4,283,562 discloses that branched-alkylphenylphosphine or cycloalkylphenylphosphine ligands can be employed in a rhodium catalyzed hydroformylation process in order to provide a catalyst which is more stable against intrinsic deactivation. U.S. Pat. No. 4,400,548 discloses that bisphosphine monoxide ligands can be employed to provide rhodium complex catalysts of improved thermal stability useful for the hydroformylation production of aldehydes.
However, despite the obvious benefits attendant with the teachings of the patents mentioned above, the search continues for phosphorus ligands which provide improved characteristics, particularly with regard to ligand volatility.
For example, rhodium complex catalyzed hydroformylation processes preferably are carried out in a non-aqueous hydroformylation reaction medium containing both soluble catalyst complex and free phosphorus ligand, i.e., ligand not tied to or bound to the rhodium catalyst complex. In such processes, the desired aldehyde product is separated and recovered from the reaction product medium e.g. by distillation, and in continuous liquid catalyst recycle operations, the non-volatilized catalyst-ligand containing residue is recycled to the reactor. Accordingly, effective separation and recovery of the desired aldehyde product from its hydroformylation reaction product medium without excessive loss of phosphorus ligand and catalyst complex is important. Thus, in such non-aqueous hydroformylation processes, and in particular in liquid catalyst recycle processes, the volatility of the phosphorus ligand relative to the other components in the reaction medium also is of primary concern.
Removal (stripping) of phosphorus ligand with aldehyde product during distillation separation of product from reaction medium can result in not only high phosphorus ligand loss but also adverse changes in catalyst properties and catalyst deactivation. Indeed, if the rate of such simultaneous volatilization of the phosphorus ligand with aldehyde product is too high, an additional ligand recovery/recycle scheme may be required to make the process economical.
When low molecular weight olefins, such as propylene, are hydroformylated in non-aqueous systems using conventional tertiary phosphines such as triphenylphosphine, ligand relative volatility (re aldehyde product separation) is a concern, but is not an overwhelming problem. However, this problem is increased and magnified when the process is directed to the hydroformylation of longer chain olefinic compounds (e.g., C.sub.6 to C.sub.30 alpha-olefins) for producing the corresponding higher molecular weight aldehydes. Higher temperatures necessary to volatilize these higher molecular weight aldehyde products during separation from the hydroformylation reaction product medium also cause volatilization of such ligands.
A similar problem is presented when higher boiling aldehyde condensation by-products, such as trimers, are formed during hydroformylation and are desired to be separated, e.g., from catalyst-containing hydroformylation residues with further separate recovery of the hydroformylation catalyst and ligand. In this instance, the relative volatility of the ligand to the residue is important, without regard to whether such aldehyde condensation by-products are formed during the hydroformylation of low (e.g., C.sub.2 -C.sub.5) molecular weight olefins or of high (e.g., C.sub.6 -C.sub.30) molecular weight olefins.
Use of aqueous solutions of sulfonated arylphosphine compounds, such as the sulfonated triphenylphosphine salts disclosed in EPC 163234 and U.S. Pat. Nos. 4,248,802 and 4,399,312, as the phosphorus ligand in a hydroformylation process has been proposed to facilitate the separation and recovery of the rhodium complex catalyst and thus avoid the before-mentioned problems. Such prior art methods utilize a hydroformylation reaction medium comprised of both an organic phase containing the reaction starting materials and/or products and an aqueous or water phase containing the catalyst complex and free sulfonated phosphine ligands. A single phase non-aqueous hydroformylation reaction medium is not used in these methods. For efficient operation, such aqueous or water phase type hydroformylation reaction systems typically require high reactor pressures and/or high rhodium concentrations, and may also require buffers or phase transfer reagents and/or the use of larger and more costly processing equipment.
It has further been proposed to hydroformylate olefins in a non-aqueous reaction medium employing low volatile ionic phosphine ligands and a rhodium-phosphine ligand complex catalyst such as disclosed e.g., in U.S. Pat. Nos. 4,633,021 and 4,731,486 and such ligands can provide decided advantages in comparison to nonionic phosphine ligands. However, the search for other non-volatile phosphorus ligands which will provide at least similar, if not even better overall advantages, than such ionic phosphines remains a continuing one in the art of transition metal catalysis, and particularly in the olefin hydroformylation art.